The present disclosure relates generally to ultrasound imaging systems and methods of making and using such systems. Ultrasound imaging systems, such as intravascular ultrasound (“IVUS”) and intracardiac echo (“ICE”) imaging systems, provide visual indicia to a practitioner when diagnosing and treating various diseases and disorders. For example, intravascular ultrasound (“IVUS”) imaging systems have been used to diagnose blocked blood vessels and to provide information to a practitioner in selecting and placing stents and other devices to restore or increase blood flow to a vessel. IVUS imaging systems have also been used to diagnose plaque build-up in the blood vessels and other intravascular obstructions. Intracardiac echo (ICE) imaging systems are used to monitor one or more heart chambers. Ultrasound imaging systems can be used to visualize images of vascular tissue that are typically visualized using other imaging techniques such as angiography.
An ultrasound imaging system can include a control module, a catheter, and at least one transducer disposed in the catheter. The catheter is configured and arranged for percutaneous insertion into a patient. The catheter can be positioned in a lumen or cavity at or near a region to be imaged, such as a blood vessel wall. Electrical pulses generated by the control module are delivered to the transducer to generate acoustic pulses that are transmitted through the blood vessel wall or other patient tissue. The reflected pulses generated by these acoustic pulses are absorbed by the transducer and transformed into an electrical signal that is converted to an image visible by the practitioner.
Intravascular ultrasound imaging systems (IVUS) typically use short wavelength, high frequency (e.g., 40 MHz) ultrasound to obtain high resolution images of tissues that lie within about 10 mm of the ultrasound transducer. Intracardiac echo (ICE) imaging systems typically use longer wavelength, lower frequency (e.g., 9 MHz) ultrasound to image the walls and structures within a heart chamber that lie within about 300 mm of the ultrasound transducer.
In some procedures where tissue ablation is required, it may be desirable to use a catheter provided with an ablation tip. Examples of ablation catheters including an ablation tip are described, for example, in U.S. Pat. Nos. 5,571,088, 6,352,534, and 7,488,289, each of which is incorporated herein by reference in its entirety for all purposes. In some instances, it may be desirable to have a means for viewing the tissues adjacent to the ablation tip during the ablation procedure. For example, in ablation of tissues of the heart wall to treat arrhythmias, it is important for the ablation to extend through the wall (i.e., transmural ablation), but it is equally important to avoid ablation of sensitive structures, such as the esophagus or the phrenic nerve, that lie just behind the heart wall tissue being ablated. A means of visualizing both the direction and the progression of the ablation is therefore needed.